Various known teats have been designed to mimic the human breast in operation. One known teat is described in U.S. Pat. No. 6,645,228 and includes a stem and a base. The base has a bulbous region and an areola region from which the stem projects. The bulbous region has an upper region with a progressively thinning wall which acts as a spring element such that as an infant sucks on the teat the areola and stem move back and forth relative to the bulbous region.
Various problems arise with this arrangement. Movement of the areola region and stem relative to the bulbous region does not closely mimic the movement of the human breast during sucking Furthermore because flexibility is provided upon a progressively thinning wall region, the amount of flexing and the point at which flexing takes place is undefined and unpredictable.
A second known teat is described in U.S. Pat. No. 6,745,912 B2 (Pigeon) including a series of parallel annular grooves on the inner surface of the nipple which allows stretching of the nipple but only in a constrained direction, and with the risk of flow blockage if the nipple collapses.
In addition, efforts are continuing to provide valved feeding bottles, in particular to allow air ingress to the teat. It is believed that this reduces the risk of colic which can otherwise occur as a result of negative pressure building up in the feeding bottle. Various known arrangements include slit valves of various types, however these are frail and difficult to machine. In another approach described in German patent DE19716535 a teat is provided with an inner annular resilient flange at its base which rests on a bottle rim when screwed down by a collar. Upon a negative pressure building up inside the drinking vessel the flange lifts from the vessel rim and air passes up through the collar and between the flange and the vessel rim.
In a similar arrangement described in European patent application EP151862 a teat includes a downwardly depending cylindrical flange at its base which seals against the inner top face of a vessel neck when deformed by being screwed down by a collar. Again a negative pressure inside the vessel lifts the flange away from the vessel neck so that air flows through the collar and between the neck and the flange into the vessel to relieve the pressure differential. Such arrangements rely on the correct amount of screw pressure being applied by the user on fixing the teat which can give rise to varied levels of valving between uses. Furthermore the introduction of a circumferential flange increases material costs.